In WO-A-91/00-747, there is disclosed a rotary device having interacting rotors which have a helical form in their axial direction.
In an internal combustion engine using such a rotary device, there are separate rotary compression and expansion sections.
In a fluid compressor, the rotor pairs serve to compress and deliver compressible fluids into receivers in which the receiver pressure is substantially greater than that of the fluid source. Power is supplied by an external prime mover in order to drive the rotor pair and thus to compress the fluid, raising its pressure from that of the supply source to that of the receiver. For efficient operation of a positive displacement compressor, it is desirable to raise the pressure of the fluid charge to a level equal to that of the receiver before beginning to deliver the charge into the receiver. In the rotor system disclosed in WO-A-91/06747, there is a port in a side wall. Opening of the port is effected when the leading edge of a transfer passage in the rotor passes over the approach side of the port in the side wall. The timing of the opening of the port for the start of delivery of the charge is therefore determined by the location of the passage at a predetermined position in the recess of one rotor and is therefore incapable of adjustment during operation of the compressor. It is desirable to have means to adjust the initial charge volume so as to ensure equalisation of the charge pressure with that of the receiver at the instant at which the port begins to open. This is particularly important when the compressor does not operate with a reed valve and when the pressures of the fluid supply source and/or the receiver are not constant.
In a rotary internal combustion engine having rotor systems as disclosed in WO-A-91/06747, the rotors serve as positive and negative displacement systems, thereby effecting the volume changes which take place in the working fluid throughout the thermodynamic cycle of the engine. Most applications of internal combustion engines require power to be delivered over a range of shaft speeds and at varying torque loads. For internal combustion engines other than compression-ignition types, variation of the output power and engine speed is effected by varying the mass of working fluid used during the cycle. It is therefore desirable to provide means for varying the volume, and therefore the mass, of working fluid entrapped at the start of the cycle.
In both rotary devices of this type, i.e. in both compressor and internal combustion engine applications, it is desirable to be able to vary the maximum volume or mass of the charge during operation of the rotors.